The present invention relates to a control apparatus to control an input and output to/from a process, and particularly to a control apparatus that requires an accurately controlled period.
In the past, a control apparatus has been required to mount with a control operating system to realize the accurately controlled period. To this end, this control apparatus has provided a simplicity of scheduling, such as a suppression for an interrupt from an external device and a prohibition for a preemption, so that the control apparatus has carried out to control such that a protection from time pressure relative to tasks, such as a control period, is first prioritized.
The preemption is a function and means that a priority is set to the task to dynamically switch over execution sequences of the task. That is, this function is that the task presently in execution is halted to then execute a high priority task in first, when the high priority task becomes executable.
However, it is not necessary to operate all of the controls by an accurate period, and the control is frequently used with a low priority control, a slow control used for chemical plants, a communication control, and an event-driven control.
The event-driven control is used for supporting an event caused by the interrupt from the external devices, such as network devices, and also supporting a preemptive multitask etc. In this case, the control apparatus mounting with an information operating system is therefore used for such that it is adapted to a task having a low time pressure.
In the case of practically operated process controls, there have been installed with two types of the control apparatus: a control apparatus mounting with a control operating system; and a control apparatus mounting with the information operating system.
In addition, JP-A-2003-67201 has proposed a technique to manage such that a plurality of tasks are divided into a communication task group, a control task group, and a management task group that manages the foregoing groups. In the case of this technique, the execution sequence for the plurality of tasks is switched over for every group thereof, and CPU (Central Processing Unit) then executes a process of either information acquired from LAN (Local Area Network) or information acquired from devices, in accordance with the tasks that are switched over.